1. Field of the Invention
The present invention relates to a method for making an antimicrobial elastomeric material containing an antimicrobial composition such as a dispersion of silver oxide that is suitable for implantation within the body
2. Prior Art
Medical devices, particularly implantable elastomeric prostheses which are used in environments where micro-organisms are actively growing, can become covered with a biofilm comprising a colonized layer of microorganisms such that the function of the prosthesis is impaired. After growth of the biofilm microbial layer, filaments can grow and descend into the body or wall of the prosthesis and detrimentally affect its physical properties until the device no longer functions. The fouled device must be cleaned or discarded.
Whenever a prosthesis is in contact with moisture in a warm, nutrient rich environment, the surfaces of the prosthesis may support microbial growth which may include, inter alia, bacteria. The microbial growth can interfere with the functioning of the prosthesis, requiring removal of the prosthesis for disposal or cleaning. The microbial growth is a persistent problem in the management and care of patients who have had their larynx removed and utilize a voice prosthesis since the prosthesis is exposed to a non-sterile, humid, warm, nutrient rich environment.
Various methods for preventing microbial growth on an indwelling device have been proposed. One approach for reducing bacterial infection encountered with the use of medical devices inserted into body cavities has been to apply an antimicrobial coating to the surface of the medical device. For example, U.S. Pat. No. 4,592,920 to Murtfeldt; U.S. Pat. No. 4,603,152 to Laurin et al and U.S. Pat. No. 4,677,143 to Laurin et al. each teach applying a coating containing an antimicrobial agent such as silver oxide to the outer surfaces of medical devices such as catheters, enteral feeding tubes, endotracheal tubes and other hollow tubular devices. The '920 patent to Murtfeldt is primarily concerned with providing a surface coating of an antimicrobial metal compound on a medical device such as a catheter, but also discloses that the metal compound can be “imbedded” within the entire catheter. However, the Murtfeldt patent teaches that the imbedded construction is less desirable since the antimicrobial metal compound imbedded within the side wall of the catheter has less likelihood of encountering migrating microbes and, by inference, is less effective than a surface coating.
Seder et al., in pending U.S. patent application Ser. No. 09/833,961, the content of which is incorporated herein by reference thereto, teach that antimicrobial agents can be compounded (i.e., embedded) into those portions of a prosthesis that are not in contact with tissue. The antimicrobial portions remain free of microbial growth for an extended period which contributes to longer use of the prosthesis in vivo. For example, the valve in most voice prostheses is not in contact with tissue. It is only in intermittent contact with body fluids. The same is true of the inside surface of the tubular prosthesis and/or the facial and inside surfaces of rings or cartridges that are present to reinforce the soft body of a prosthesis. By adding an amount of microbial agent effective to resist growth onto (or into) the valve, ring or cartridge, it is found that microbial growth is delayed for a significant period without any evidence of irritation or toxicity to the tissue. Seder et al. further teach that the antimicrobial agent-bearing elastomer can be compounded by dispersion of the antimicrobial agent into the raw elastomer material. For example, silicone elastomer can contain at least 10 percent of an antimicrobial agent such as silver, or silver compounds such as silver oxide. Other suitable antimicrobial compounds such as, for example, gold, platinum, copper, zinc metal powder or oxides and salts thereof, can be used in the non-tissue contacting portions of the prosthesis. A more complete discussion of prior art methods for incorporating antimicrobial agents into, or upon, a prosthesis is also presented in Seder et al.
A problem with prior art methods of dispersing an antimicrobial agent such as Ag2O into an elastomer prior to forming a prosthetic article therefrom is the short work-time available for forming the elastomer into a prosthesis, or a portion thereof, after compounding; sometimes the work-time being as short as a minute or two. It is, therefore, desirable to provide a method for incorporating an antimicrobial agent such as, for example, silver oxide, into an elastomer such as silicone that provides a longer work-time for fabricating an article therefrom.